Men have nipples because, at an early point in the formation of an embryo, it is NEITHER sex and has the proper cells to grow into whatever is needed. I have no idea if men could breastfeed; possibly if they were given the appropriate hormone treatment the milk glands would activate -- but I don't know.
How are men suppose to breastfeed when their bodies possibly can't even produce? And anyways that would be horrifying to see a man trying to breastfeed. Women were created for that purpose not men and reason why is because it comes with them during the embryo development. And word of speaking just saying I think it would look awfully weird of a guy not having nipples LMFAO!!!! xD